I normally load Clays or ClayDot gunpowder for shotgun loads for Cowboy with the intent to replicate "FeatherLite" LNLR shells which have a velocity of 980 FPS. I use 1 oz. of shot because I like to....some people load 3/4 or 7/8 oz. and that's fine for them. With Clays and Claydot powder being really scarce and other "old faithful" powders in short supply I ran across Perfect Pattern gunpowder from Hodgdon which is readily available.  You can find load data on Hodgdon's website for this powder.